|The authors present modifications to the dust representation in the WRF-Chem model and its GOCART module. The effects of the modifications are discussed and comparisons with observations show that they can result in a more realistic AOD and PM10. This makes the article valuable for everyone using WRF-Chem and GOCART for dust modelling so that it is worth publishing after considering the following comments.|
The modification addressing the problem in the gravitational settling clearly fixes an error in the algorithm. In contrast, the other modifications are essentially adjustments of parameters describing the size distribution within the size bins. While they look reasonable and can improve the results, I suggest to reconsider using the terms "inconsistency" or "error" in this context. Generally, when discussing the sub-bin distribution, one naturally reaches the limits of a bin model. The authors assume that within each bin the mass distribution density as a function of ln(r) is constant. Considering that peaks in the size distributions often resemble log-normal distributions, this is reasonable if the bin represents the centre of a peak, but it remains an assumption with limitations. For example, it corresponds to, in terms of r, a density increase towards smaller r with 1 / r, which may lead to artificially high concentrations of small particles towards the lower end of the size bin. Is the assumption used consistently for all other radius dependent processes, like gravitational settling?
Page 6 line 6
The adjustment of the emission size distribution according to observations is presented very briefly as part of the tuning. Isn't the relevance of this improvement on par with that of the adjustments in sections 3.1 and 3.2?
Page 7 line 17, page 10 line 4, page 10 Table caption etc.
The formulation "size distributions are functions of the natural logarithm of particle radius" or similar is not very clear, I suggest something like "size distribution in terms of the natural logarithm of the radius is considered constant within each bin" or to make explicitly use of the expression dV / dlnr as on page 5 line 24.
Page 9 lines 1 and 2
Please mention that the numbers represent diameters, or better convert to radii to be consistent with the GOCART numbers in Table 1.
Page 9 line 9
Where exactly comes the value 0.46 um from?
Page 9 Table 4 and page 10 Table 5
There is plenty of redundant information, you can combine Tab 4 a, b and Tab 5 b into one table. Units are missing.
Page 23 Eq. (C2)
Please check, does the RHS yield z or Delta z?